DivineInject.github.io/why.html at master · DivineInject/DivineInject.github.io · GitHub

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        <h1>
<a id="divine-inject" class="anchor" href="#divine-inject" aria-hidden="true"><span class="octicon octicon-link"></span></a>Why?</h1>

<p>Why did we create DivineInject? Because dependency injection is important - but done wrong it can do more harm than good.
DivineInject is opinionated about the right way to use dependency injection:</p>

<ul>
<li>
<p><b>Constructor injection or death</b></p>

<p>Setter injection is bad for your health, just say no</p>
</li>
<li>
<p><b>Dependencies are singletons</b></p>

<p>Dependencies are external to your application - your DI framework doesn't need to know about users or sessions or threads.</p>
</li>
<li>
<p><b>Domain objects can be rich, too</b></p>

<p>Your domain model doesn't have to be <a href="https://en.wikipedia.org/wiki/Anemic_domain_model">anemic</a></p>
</li>
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<h2>
<a id="constructor-injection" class="anchor" href="#constructor-injection" aria-hidden="true"><span class="octicon octicon-link"></span></a>Constructor Injection</h2>

<p>Setter and method injection are much harder to get right - so DivineInject simply doesn't support them. If you can't implement your dependencies as
constructor arguments, then maybe you should refactor the dependency so you can.</p>

<h2>
<a id="singleton-dependencies" class="anchor" href="#singleton-dependencies" aria-hidden="true"><span class="octicon octicon-link"></span></a>Singleton Dependencies</h2>

<p>Dependencies are <b>external</b> to your application. Things like users and sessions are domain concepts in <i>your</i> domain, not in
the domain of dependency injectors. All dependency injection frameworks get wrapped up in different scopes, which makes the frameworks harder to use.
Divine Inject simply doesn't support them &mdash; if you need something user-scoped or session-scoped, then implement the logic yourself. It isn't hard,
and if you ever want to understand the lifecycle of your objects it's in <i>your code</i>, not mine &mdash; which will make reasoning about your code or
debugging it a million times easier.</p>

<h2>
<a id="rich-domain-objects" class="anchor" href="#rich-domain-objects" aria-hidden="true"><span class="octicon octicon-link"></span></a>Rich Domain Objects</h2>

<p>DivineInject borrows an idea from <a href="https://github.com/google/guice">Google Guice</a> - with Guice it is called "assisted injection", in
DivineInject we call it <i>generated factory injection</i>. The idea is the same &mdash; providing a simple way to create objects with constructors
which accept runtime arguments as well as dependencies to inject. This allows you to create <a href="rich_domain_objects.html">rich, stateful
domain objects</a> which also have dependencies.</p>

<hr/>

<p>Find out more about these ideas in the detailed <a href="getting_started.html">getting started</a> guide.</p>
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